1. Field of the Invention
The present invention relates to a system for transferring data between blocks, and more particularly to blocks constructing a time division multiplexer used preferably for a so-called multi-media communication system.
In general, a time division multiplexer is constructed by a plurality of blocks so as to increase the number of channels to be accommodated in the multimedia communication system which handles both digital data of, e.g., computers, televisions, and facsimiles, and digital signals such as telephone speech signals. Further, the blocks are usually connected to each other via a two-way data bus which transfers the bits of data in parallel, i.e., a parallel data transfer.
In such a time division multiplexer, it is desired to further increase efficiency of data transfer between the blocks.
2. Description of the Related Art
The prior art system for transferring data between blocks will be explained in detail hereinafter, and an outline thereof will be given below.
The prior art system employed in a time division multiplexer is primarily comprised of transfer control units, contained in each block, and a two-way data bus for connecting the blocks to each other. Each of the transfer control units is constructed with both two-way gate circuits and a direction control unit which cooperates with the corresponding two-way gate circuits. Thus, two-way data communication can be achieved between every two blocks through the two-way data bus.
The above-mentioned prior art system, however, produces some problems, as will be described below. The media to be accommodated in the time division multiplexer is not limited to single information, such as a telephone speech signal only, but a variety of information including picture signals, video signals and the like can be accommodated. In this case, a variety of transmission speeds exist in the multiplexer in correspondence with respective information to be transferred. Therefore, it is necessary to adopt a variety of constructions for the multiplexer in order to cope with the variety of media information. A first problem arises here that, when a variety of multiplexers are prepared for respective media information, the manufacturing cost rises due to the increased variety but reduced amount of production.
The transfer control units of the prior art are operative only to change the direction of transfer of data, as a whole, under control of the aforesaid direction control units. Therefore, even if the number of the parallel transfer data bits is smaller than the number of bit lines of the two-way data bus, in a case where a low transmission speed data is handled, the whole group of bit lines of the data bus is occupied by the low transmission speed data which is usually composed of a smaller number of bits than the number of bit lines of the two-way data bus. A second problem arises here that efficiency of data transfer through the two-way data bus is reduced due to the above-mentioned redundant occupation of the data bus.
Further, in a case where many blocks are mounted in the multiplexer, a mixture of both high transmission speed data and low transmission speed data is often transferred on the data bus. A third problem arises here that the number of channels to be accommodated in the multiplexer is limited to some extent since the data bus cannot be used, in such case, with high efficiency.